Fuel cells are electrochemical devices which can convert energy stored in fuels to electrical energy with high efficiencies. Electrolyzer cells are electrochemical devices which can use electrical energy to reduce a given material, such as water, to generate a fuel, such as hydrogen. The fuel and electrolyzer cells may comprise reversible cells which operate in both fuel cell and electrolysis mode.
In a high temperature fuel cell system, such as a solid oxide fuel cell (SOFC) system, an oxidizing flow is passed through the cathode side of the fuel cell, while a fuel flow is passed through the anode side of the fuel cell. The oxidizing flow is typically air, while the fuel flow can be a hydrocarbon fuel, such as methane, natural gas, propane, ethanol, or methanol. The fuel cell, operating at a typical temperature between 750° C. and 950° C., enables combination of the oxygen and free hydrogen, leaving surplus electrons behind. The excess electrons are routed back to the cathode side of the fuel cell through an electrical circuit completed between anode and cathode, resulting in an electrical current flow through the circuit.
Fuel cell stacks may be either internally or externally manifolded for fuel and air. In internally manifolded stacks, the fuel and air is distributed to each cell using risers contained within the stack. In other words, the gas flows through openings or holes in the supporting layer of each fuel cell, such as the electrolyte layer, and gas separator of each cell. In externally manifolded stacks, the stack is open on the fuel and air inlet and outlet sides, and the fuel and air are introduced and collected independently of the stack hardware. For example, the inlet and outlet fuel and air flow in separate channels between the stack and the manifold housing in which the stack is located.
Fuel cell stacks are frequently built from a multiplicity of cells in the form of planar elements, tubes, or other geometries. Fuel cell stacks, particularly those with planar geometry, often use seals between electrolyte and interconnect surfaces to contain fuel and air at various locations within the stack. As shown in FIG. 1, in fuel cell stacks that are internally manifolded for fuel (i.e., in which fuel is provided through fuel riser openings in SOFCs and interconnects in the stack) electrolyte crack formation has been observed at ring seals initiated by cell electrolyte corrosion. A ring seal is a seal that surrounds the fuel inlet and fuel outlet riser openings between the cathode (i.e., air) side of a given SOFC and an air side of an adjacent interconnect (also known as a gas separator plate). This corrosion in conjunction with stresses which occur during operation lead to cracks, cell cracking and catastrophic failure at elevated temperatures (e.g., after 2 hours at 900 C.) as shown in FIG. 2.